﻿/*----------------------------------------------------------------
 * 
 * 版权所有：Copyright (C) 2013
 * 
 * 文件名：PredicateExtension.cs
 * 文件功能描述：
 * 
 * 
 * 作 者：zhangq
 * 邮 箱：ifunnyface@outlook.com
 * 日 期：2013-01-08 10:23:49
 * 
 * 
 * 修改标识： Author
 * 修改描述： 相关描述
 * 
 * ---------------------------------------------------------------- */

using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Text;

namespace Common.Extensions.Where
{

    /// <summary>
    /// 
    /// </summary>
    public static class PredicateExtension
    {

        public static Expression<Func<T, bool>> True<T>() { return f => true; }

        public static Expression<Func<T, bool>> False<T>() { return f => false; }

        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> exp_left, Expression<Func<T, bool>> exp_right)
        {
            var candidateExpr = Expression.Parameter(typeof(T), "candidate");
            var parameterReplacer = new ParameterReplacer(candidateExpr);

            var left = parameterReplacer.Replace(exp_left.Body);
            var right = parameterReplacer.Replace(exp_right.Body);
            var body = Expression.And(left, right);

            return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
        }

        public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> exp_left, Expression<Func<T, bool>> exp_right)
        {
            var candidateExpr = Expression.Parameter(typeof(T), "candidate");
            var parameterReplacer = new ParameterReplacer(candidateExpr);

            var left = parameterReplacer.Replace(exp_left.Body);
            var right = parameterReplacer.Replace(exp_right.Body);
            var body = Expression.Or(left, right);

            return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
        }

         
    }

}